JP2007003554A - Variable power optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable power optical system that ensures a wide angle and a superhigh variable power although high performance/miniaturization is achieved, and to provide an imaging apparatus that has the variable power optical system. <P>SOLUTION: The variable power optical system for forming an optical image of an object onto the light receiving face of an imaging element so that a power is variable includes at least, in order from the object side, a first lens group Gr1 with a positive power, a second lens group Gr2 with a negative power, a third lens group Gr3 with a positive power, and a fourth lens group Gr4 with a positive power. In addition, at least the first lens group Gr1 and the third lens group Gr3 move when the power is varied, and the first lens group Gr1 moves to the object side when the power is varied from the wide-angle end (W) to the tele-photo end (T). The variable power optical system satisfies the following conditional expressions: -0.5<m2/fw<5.0, 7.0<f1/fw<20.0, and 0.05<f3/ft<0.4 (m2 denotes an amount of relative movement of the second lens group when the power is varied from the wide-angle end to the telephoto end (movement to the object side is positive), f1 denotes the focal distance of the first lens group, f3 denotes the focal distance of the third lens group, fw is the focal distance of the entire system at the wide-angle end, and ft denotes the focal distance of the entire system at the telephoto end). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a variable magnification optical system, for example, a variable magnification optical system suitable for a digital camera that captures an image of a subject with an image sensor or a digital device with an image input function (in particular, a small zoom lens with a wide angle and a high variable magnification). The present invention relates to a lens system) and an image pickup apparatus including the same.

In recent years, with the spread of personal computers, digital cameras that can easily capture images are becoming popular. Along with this, a smaller digital camera has been demanded, and further downsizing of the photographing lens system has been demanded. On the other hand, since the number of pixels of the image sensor tends to increase year by year, the photographic lens system is required to have high optical performance corresponding to the increase in the number of pixels of the image sensor and ease of manufacturing that can correspond to shortening of the product cycle. . In addition, high zoom ratios with zoom ratios exceeding 7 times or 10 times have been generalized, and further high zoom ratios are expected, but there are also expectations for wide angle. Various types of zoom lens systems have been proposed in the past to meet these requirements (see, for example, Patent Documents 1 to 4).
JP-A-63-266414 JP-A-8-82743 JP 2002-98895 A Japanese Patent Laid-Open No. 2004-212512

  However, conventionally proposed zoom lens systems are difficult to simultaneously satisfy the conflicting demands of further higher zooming, smaller size, higher performance, and wide angle. For example, in the zoom lens system proposed in Patent Document 1, the zoom ratio is about 10 times, which is difficult to say as high zoom ratio. In the zoom lens system proposed in Patent Document 2, although the zoom ratio is as large as 20 times, the angle of view is 70 degrees or less, which is difficult to say. Also, in the zoom lens systems proposed in Patent Documents 3 and 4, it cannot be said that the balance of zoom ratio, optical performance, overall lens length, and the like is good.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a variable-power optical system having a wide angle and a super-high magnification while having a high performance and a small size, and an imaging apparatus including the same. There is.

In order to achieve the above object, a variable magnification optical system according to a first aspect of the present invention is a variable magnification optical system for forming an optical image of an object on a light receiving surface of an image sensor so that the magnification can be changed. In order, it includes at least a first lens group having a positive power, a second lens group having a negative power, a third lens group having a positive power, and a fourth lens group having a positive power, At the time of zooming, at least the first lens group and the third lens group move, and at zooming from the wide angle end to the telephoto end, the first lens group moves toward the object side, and the following conditional expressions (1), ( It satisfies 2) and (3).
-0.5 <m2 / fw <5.0 (1)
7.0 <f1 / fw <20.0 (2)
0.05 <f3 / ft <0.4 (3)
However,
m2: Relative amount of movement of the second lens unit during zooming from the wide-angle end to the telephoto end (movement toward the object side is positive),
f1: focal length of the first lens group,
f3: focal length of the third lens group,
fw: focal length of the entire system at the wide-angle end,
ft: focal length of the entire system at the telephoto end,
It is.

  In a variable magnification optical system according to a second invention, in the first invention, the second lens group has at least one negative lens and one positive lens, and at least one of the negative lenses has an aspherical surface. It is characterized by that.

A variable magnification optical system according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, the following conditional expression (4) is satisfied.
0.05 <f3 / f4 <0.8 (4)
However,
f4: focal length of the fourth lens group,
It is.

A variable magnification optical system according to a fourth invention is characterized in that, in any one of the first to third inventions, the following conditional expression (5) is satisfied.
-0.2 <f2 / ft <-0.02 (5)
However,
f2: focal length of the second lens group,
It is.

  A variable magnification optical system according to a fifth aspect of the present invention is the optical system according to any one of the first to fourth aspects, wherein the fifth lens group includes a fifth lens group having a positive power on the image side of the fourth lens group. In the variable power optical system having the configuration, the position of the fifth lens group is fixed in zooming from the wide-angle end to the telephoto end.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the fifth lens group comprises a single positive lens.

  An image pickup apparatus according to a seventh invention is characterized by including the variable magnification optical system according to any one of the first to sixth inventions.

  According to the present invention, in the variable magnification optical system including the four components of positive, negative, positive, and positive in order from the object side, the power of the moving group and the like satisfy a predetermined condition. While achieving high performance, it is possible to achieve wide angle and ultra high zoom ratio. Therefore, it is possible to realize an image pickup apparatus including a small-sized, high-performance, wide-angle, and ultra-high variable power optical system. If the imaging apparatus according to the present invention is used in devices such as a digital camera, it can contribute to thinning, lightening, compactness, cost reduction, high performance, high functionality, etc. of these devices.

  Hereinafter, a variable magnification optical system, an imaging apparatus, and the like embodying the present invention will be described with reference to the drawings. An imaging apparatus according to the present invention is an optical apparatus that optically captures an image of a subject and outputs it as an electrical signal, and constitutes a main component of a camera used for still image shooting and moving image shooting of a subject. is there. Examples of such cameras include digital cameras, video cameras, surveillance cameras, in-vehicle cameras, video phone cameras, door phone cameras, etc., and personal computers, portable information devices (mobile computers, mobile phones, mobile phones). Cameras that are built in or externally attached to information terminals (PDA: Personal Digital Assistant) and other small and portable information device terminals, peripheral devices (mouse, scanner, printer, memory, etc.), and other digital devices Can be mentioned. As can be seen from these examples, it is possible not only to configure a camera by using an imaging apparatus, but also to add a camera function by mounting the imaging apparatus on various devices. For example, a digital device with an image input function such as a mobile phone with a camera can be configured.

  The term “digital camera” used to refer to the one that records optical still images exclusively, but digital still cameras and home digital movie cameras that can handle still images and movies simultaneously have also been proposed. In particular, it has become difficult to distinguish. Therefore, the term “digital camera” means a digital still camera, digital movie camera, or web camera (whether an open type or a private type, a camera that is connected to a network and connected to a device that enables image transmission / reception). , And the like, including those directly connected to a network and those connected via a device having an information processing function such as a personal computer.) It is assumed that all cameras having an imaging device including an imaging device or the like for converting a video signal as an electric video signal as main components are included.

  FIG. 11 is a schematic cross-sectional view showing a schematic optical configuration example of a camera CU (corresponding to a digital camera, a digital device with an image input function, etc.). An imaging device LU mounted on the camera CU is a zoom lens system ZL (magnification as a photographing lens system) that forms an optical image (IM: image plane) of the object in order from the object (namely, subject) side. ST corresponds to an optical system, ST: stop, and parallel plane plate PT (optical filters such as an optical low-pass filter and an infrared cut filter disposed as necessary; corresponding to a cover glass of the image sensor SR) And an imaging element SR that converts an optical image IM formed on the light receiving surface SS by the zoom lens system ZL into an electrical signal, and forms a part of a camera CU corresponding to a digital camera or the like. Yes. When a digital camera is configured with this image pickup device LU, the image pickup device LU is usually arranged inside the body of the camera. However, when realizing the camera function, it is possible to adopt a form as necessary. is there. For example, the unitized imaging device LU may be configured to be detachable or rotatable with respect to the camera body, and the unitized imaging device LU may be detachable with respect to a portable information device (cell phone, PDA, etc.) or You may comprise so that rotation is possible.

  The zoom lens system ZL includes a plurality of lens groups, and the plurality of lens groups moves along the optical axis AX and performs zooming (ie, zooming) by changing the lens group interval. In the first, second, fourth, and fifth embodiments, which will be described later, the zoom lens system ZL has a positive / negative / positive / positive / positive five-component zoom configuration. In the third embodiment, zooming is performed. The lens system ZL has a positive / negative / positive / positive four-component zoom configuration. In any of the embodiments, the first to fourth lens groups Gr1 to Gr4 constitute a moving group, and the fifth lens group Gr5 is fixed in the first, second, fourth, and fifth embodiments. It constitutes a group. Note that the photographing lens system used in the imaging device LU is not limited to the zoom lens system ZL. Instead of the zoom lens system ZL, another type of variable magnification optical system (for example, a variable focal length imaging optical system such as a varifocal lens system or a multiple focal length switching type lens) may be used as a photographing lens system. .

  An optical image to be formed by the zoom lens system ZL passes through an optical low-pass filter (corresponding to the parallel plane plate PT in FIG. 11) having a predetermined cutoff frequency characteristic determined by the pixel pitch of the image sensor SR. By doing so, the spatial frequency characteristic is adjusted so that the so-called aliasing noise generated when converted into an electrical signal is minimized. Thereby, generation | occurrence | production of a color moire can be suppressed. However, if the performance around the resolution limit frequency is suppressed, there is no need to worry about the occurrence of noise without using an optical low-pass filter, and the display system where the noise is not very noticeable (for example, the liquid crystal of a mobile phone) When a user performs shooting or viewing using a screen or the like, it is not necessary to use an optical low-pass filter in the shooting lens system.

  As the optical low-pass filter, a birefringence low-pass filter, a phase low-pass filter, or the like can be applied. Examples of the birefringent low-pass filter include those made of a birefringent material such as quartz whose crystal axis direction is adjusted to a predetermined direction, and those obtained by laminating wave plates that change the polarization plane. Examples of the phase type low-pass filter include those that achieve the required optical cutoff frequency characteristics by the diffraction effect.

  As the imaging element SR, for example, a solid-state imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor having a plurality of pixels is used. The optical image formed by the zoom lens system ZL (on the light receiving surface SS of the image sensor SR) is converted into an electrical signal by the image sensor SR. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, etc. as necessary, and recorded as a digital video signal in a memory (semiconductor memory, optical disk, etc.), or in some cases via a cable. Or converted into an infrared signal and transmitted to another device.

  In the imaging apparatus LU shown in FIG. 11, the zoom lens system ZL performs reduction projection from the enlargement subject to the reduction-side imaging element SR, but a display element that displays a two-dimensional image instead of the imaging element SR. If a zoom lens system ZL is used as a projection lens system using a liquid crystal display element (for example, a liquid crystal display element), an image projection apparatus that performs enlargement projection from the image display surface on the reduction side to the screen surface on the enlargement side can be configured. That is, the zoom lens system ZL of each embodiment described below is not limited to use as a photographing lens system, but can also be suitably used as a projection lens system.

  FIGS. 1 to 5 are lens configuration diagrams respectively corresponding to the zoom lens systems ZL constituting the first to fifth embodiments, and the lens arrangement at the wide angle end (W) is shown in an optical section. In each lens configuration diagram, the surface with ri (i = 1, 2, 3,...) Is the i-th surface counted from the object side (the surface with ri marked with * is an aspheric surface). In addition, the axial upper surface interval with di (i = 1, 2, 3,...) Is a variable interval that changes during zooming among the i-th axial upper surface interval counted from the object side. In each lens configuration diagram, arrows m1, m2, m3, and m4 indicate the first lens group Gr1, the second lens group Gr2, the third lens group Gr3, and the third lens group Gr3 in zooming from the wide-angle end (W) to the telephoto end (T). The movement of the four lens groups Gr4 is schematically shown. The arrow mL on the most image side indicates the plane parallel plate PT and further the fifth lens group Gr5 (first, second, fourth, and fifth embodiments). ) Indicates that the position is fixed during zooming. In any of the embodiments, the third lens group Gr3 has a stop ST closest to the object side, and the stop ST is configured to zoom as a part of the third lens group Gr3 (arrow m3). ing.

  The zoom lens systems ZL of the first, second, fourth, and fifth embodiments have a first lens group Gr1 having positive power (power: an amount defined by the reciprocal of the focal length) in order from the object side. A second lens group Gr2 having a negative power, a third lens group Gr3 having a positive power, a fourth lens group Gr4 having a positive power, a fifth lens group Gr5 having a positive power, The zoom lens has a five-component zoom configuration in which zooming is performed by changing the distance between lens groups. The zoom lens system ZL according to the third embodiment includes, in order from the object side, a first lens group Gr1 having a positive power, a second lens group Gr2 having a negative power, and a first lens group Gr2 having a positive power. The zoom lens includes a three-lens group Gr3 and a fourth lens group Gr4 having positive power, and has a four-component zoom configuration in which zooming is performed by changing the distance between the lens groups. The lens configuration of each embodiment will be described in detail below.

  In the first embodiment (FIG. 1), each lens group is configured as follows in a positive / negative / positive / positive / positive five-component zoom configuration. The first lens group Gr1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a positive meniscus lens convex on the object side, and a positive meniscus lens convex on the object side. . The second lens group Gr2 includes, in order from the object side, a negative meniscus lens that is concave on the image side, a cemented lens that includes a biconcave negative lens and a biconvex positive lens, and an image side that is concave on the object side. Negative meniscus lens. The third lens group Gr3 includes, in order from the object side, the stop ST, a biconvex positive lens whose object side surface is an aspheric surface, a negative meniscus lens concave on the image side, and a biconvex positive lens. And a negative meniscus lens having a concave surface on the image side. The fourth lens group Gr4 is composed of only one cemented lens including a biconvex positive lens and a biconcave negative lens. The fifth lens group Gr5 is composed of only one biconvex positive lens whose both surfaces are aspheric surfaces. In zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 monotonously moves to the object side, and the second lens group Gr2 moves U-turn from the object side to the image side after moving to the object side. The third lens group Gr3 moves to the object side while gradually decreasing the speed, and the fourth lens group Gr4 moves U-turns from the object side to the image side after moving to the object side. On the other hand, the fifth lens group Gr5 and the plane parallel plate PT are fixed at the zoom position with respect to the image plane IM.

  In the second embodiment (FIG. 2), each lens group is configured as follows in a positive / negative / positive / positive / positive five-component zoom configuration. The first lens group Gr1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a positive meniscus lens convex on the object side, and a positive meniscus lens convex on the object side. . The second lens group Gr2 includes, in order from the object side, a negative meniscus lens that is concave on the image side, a cemented lens that is composed of a biconcave negative lens having an aspheric object side surface and a biconvex positive lens, and a concave lens on the object side. Negative meniscus lens. The third lens group Gr3 includes, in order from the object side, the stop ST, a biconvex positive lens whose object side surface is an aspheric surface, a negative meniscus lens concave on the image side, a biconvex positive lens, and an image side surface. And a negative meniscus lens concave on the image side made of an aspherical surface. The fourth lens group Gr4 is composed of only one cemented lens including a biconvex positive lens and a biconcave negative lens. The fifth lens group Gr5 is composed of only one positive meniscus lens convex on the image side whose both surfaces are aspheric surfaces. In zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 monotonously moves to the object side, and the second lens group Gr2 moves U-turn from the image side to the object side after moving to the image side. The third lens group Gr3 moves to the object side while gradually decreasing the speed, and the fourth lens group Gr4 moves U-turns from the object side to the image side after moving to the object side. On the other hand, the fifth lens group Gr5 and the plane parallel plate PT are fixed at the zoom position with respect to the image plane IM.

  In the third embodiment (FIG. 3), each lens group is configured as follows in a positive / negative / positive / positive four-component zoom configuration. The first lens group Gr1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a positive meniscus lens convex on the object side, and a positive meniscus lens convex on the object side. . The second lens group Gr2 includes, in order from the object side, a negative meniscus lens that is concave on the image side, and a cemented lens that includes a biconcave negative lens and a positive meniscus lens that is convex on the object side. The third lens group Gr3 includes, in order from the object side, the stop ST, a positive meniscus lens convex on the object side whose object side surface is an aspheric surface, a negative meniscus lens concave on the image side, a biconvex positive lens, It consists of The fourth lens group Gr4 includes only a cemented lens including a positive meniscus lens convex on the object side having an aspheric object side surface and a negative meniscus lens concave on the image side having an aspheric image side surface. . In zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 monotonously moves to the object side, and the second lens group Gr2 moves U-turn from the image side to the object side after moving to the image side. The third lens group Gr3 moves to the object side while gradually increasing the speed, and the fourth lens group Gr4 moves U-turns from the object side to the image side after moving to the object side. The plane parallel plate PT is fixed at a zoom position with respect to the image plane IM.

  In the fourth embodiment (FIG. 4), each lens group is configured as follows in a positive / negative / positive / positive / positive five-component zoom configuration. The first lens group Gr1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a positive meniscus lens convex on the object side, and a positive meniscus lens convex on the object side. . The second lens group Gr2 includes, in order from the object side, a negative meniscus lens that is concave on the image side, a cemented lens that includes a biconcave negative lens and a biconvex positive lens, and an image side that is concave on the object side. Negative meniscus lens. The third lens group Gr3 includes, in order from the object side, the stop ST, a biconvex positive lens whose object side surface is an aspheric surface, a negative meniscus lens concave on the image side, and a biconvex positive lens. And a negative meniscus lens having a concave surface on the image side. The fourth lens group Gr4 is composed of only one cemented lens including a biconvex positive lens and a biconcave negative lens. The fifth lens group Gr5 is composed of only one biconvex positive lens whose both surfaces are aspheric surfaces. In zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 monotonously moves to the object side, and the second lens group Gr2 moves U-turn from the image side to the object side after moving to the image side. The third lens group Gr3 moves substantially monotonically toward the object side, and the fourth lens group Gr4 moves toward the object side while gradually decreasing the speed. On the other hand, the fifth lens group Gr5 and the plane parallel plate PT are fixed at the zoom position with respect to the image plane IM.

  In the fifth embodiment (FIG. 5), each lens group is configured as follows in a positive / negative / positive / positive / positive five-component zoom configuration. The first lens group Gr1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a positive meniscus lens convex on the object side, and a positive meniscus lens convex on the object side. . The second lens group Gr2 includes, in order from the object side, a negative meniscus lens that is concave on the image side, a cemented lens that includes a biconcave negative lens and a biconvex positive lens, and a negative meniscus lens that is concave on the object side. It is configured. The third lens group Gr3 includes, in order from the object side, the stop ST, a biconvex positive lens whose object side surface is an aspheric surface, a negative meniscus lens concave on the image side, and a biconvex positive lens. And a biconcave negative lens made of a spherical surface. The fourth lens group Gr4 includes only one cemented lens including a negative meniscus lens concave on the image side and a positive meniscus lens convex on the object side. The fifth lens group Gr5 is composed of only one positive meniscus lens convex on the image side whose both surfaces are aspheric surfaces. In zooming from the wide-angle end (W) to the telephoto end (T), the first lens group Gr1 monotonously moves toward the object side, and the second lens group Gr2 moves toward the object side while gradually increasing the speed. The lens group Gr3 monotonously moves toward the object side, and the fourth lens group Gr4 moves toward the object side while gradually decreasing the speed. On the other hand, the fifth lens group Gr5 and the plane parallel plate PT are fixed at the zoom position with respect to the image plane IM.

  As described above, any of the embodiments is configured to include at least four components of positive, negative, positive, and positive in order from the object side. In such a variable magnification optical system, at least the first lens group and the third lens group move during zooming, the first lens group moves toward the object side during zooming from the wide-angle end to the telephoto end, and further a moving group. If the power and the like satisfy a predetermined condition, it is possible to achieve a wide-angle and ultra-high zoom ratio of the zoom optical system while achieving miniaturization and high performance. If an imaging device equipped with the variable magnification optical system is used in a device such as a digital camera, it can contribute to its thinness, light weight, compactness, low cost, high performance, high functionality, and the like. The above conditions for achieving these effects in a well-balanced manner and achieving higher optical performance and the like will be described below. In addition, the zoom ratio when satisfying the conditions described below is preferably 10 times or more, more preferably 15 to 25 times, and still more preferably, from the balance of high performance, downsizing, widening, and the like. Is 17 to 20 times.

It is desirable to satisfy the following conditional expressions (1), (2) and (3). By satisfying conditional expressions (1), (2), and (3), it is possible to achieve compactness while ensuring sufficient optical performance, and to achieve a wide angle and high zoom ratio.
-0.5 <m2 / fw <5.0 (1)
7.0 <f1 / fw <20.0 (2)
0.05 <f3 / ft <0.4 (3)
However,
m2: Relative amount of movement of the second lens unit during zooming from the wide-angle end to the telephoto end (movement toward the object side is positive),
f1: focal length of the first lens group,
f3: focal length of the third lens group,
fw: focal length of the entire system at the wide-angle end,
ft: focal length of the entire system at the telephoto end,
It is.

  Conditional expression (1) defines a preferable condition range regarding the relative movement amount of the second lens group by a ratio with the focal length of the entire system at the wide angle end. This relative movement amount corresponds to the relative displacement amount at the telephoto end with respect to the position at the wide-angle end. Therefore, if the position of the second lens group at the wide-angle end is the same as the position of the second lens group at the telephoto end, the relative movement amount of the second lens group is zero. In zooming from the wide-angle end to the telephoto end, the relative movement amount of the second lens group is naturally zero even when the second lens group Gr2 is fixed at the zoom position with respect to the image plane IM.

  When the second lens group moves to the image side beyond the lower limit of conditional expression (1), the amount of movement of the third lens group decreases, and the magnification ratio of the third lens group decreases. Aberration correction becomes difficult if the burden of zooming of the second lens group is increased in order to keep the same zooming ratio as a whole. Conversely, if the second lens group moves toward the object side beyond the upper limit of conditional expression (1), the magnification of the second lens group becomes small. If the movement amount of the first lens group is increased in order to make the second lens group have the same magnification, it is not preferable because the total lens length increases. Alternatively, if the power of the second lens group is increased in order to make the second lens group have the same magnification, it is not preferable because aberration correction becomes difficult and error sensitivity increases.

It is more desirable to satisfy the following conditional expression (1a).
0.1 <m2 / fw <4.0 (1a)
The conditional expression (1a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (1).

  Conditional expression (2) defines a preferable condition range regarding the power of the first lens group by dividing the focal length of the first lens group by the focal length of the entire system at the wide angle end. If the lower limit of conditional expression (2) is exceeded, the positive power of the first lens group becomes strong, which is preferable in terms of downsizing and compacting the front lens diameter. Increases, and in particular, a lot of field curvature and distortion occur. In order to correct it satisfactorily, an additional number of lenses or an aspherical surface is required, which is not preferable. Conversely, if the upper limit of conditional expression (2) is exceeded, it will be advantageous in correcting aberrations, but it is not preferable because an increase in the diameter of the front lens and the accompanying increase in size cannot be avoided.

It is more desirable to satisfy the following conditional expression (2a).
8.0 <f1 / fw <17.0… (2a)
The conditional expression (2a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (2).

  Conditional expression (3) defines a preferable condition range regarding the power of the third lens group by dividing the focal length of the third lens group by the focal length of the entire system at the telephoto end. If the lower limit of the conditional expression (3) is exceeded, the positive power of the third lens group becomes strong, resulting in an increase in the amount of aberration generated in the third lens group, and particularly large spherical aberration. In order to correct it satisfactorily, an additional number of lenses, an aspherical surface, and the like are required, which is not preferable. On the contrary, if the upper limit of conditional expression (3) is exceeded, it will be advantageous in correcting aberrations, but the distance between the front and rear of the third lens group must be changed greatly during zooming, resulting in a large overall lens length. Therefore, it is not preferable.

It is more desirable to satisfy the following conditional expression (3a).
0.1 <f3 / ft <0.3 (3a)
The conditional expression (3a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (3).

  It is preferable that the second lens group has at least one negative lens and one positive lens, and at least one of the negative lenses has an aspherical surface. When attempting to reduce the size, increase the zoom ratio, and widen the angle, the power of the second lens group becomes strong negative and a large negative aberration occurs. However, at least one of the negative lenses in the second lens group has an aspherical surface. Using this makes it possible to correct aberrations satisfactorily. From this viewpoint, a negative lens having an aspherical surface is used for the second lens group Gr2 of the first, second, and fourth embodiments.

  As described above, the aspherical surface of the negative lens used in the second lens group preferably has a shape such that the negative power of the negative lens becomes weaker from the center toward the periphery. When attempting to reduce the size and widen the angle, the power of the second lens group becomes stronger, and the aberrations that occur (especially negative distortion at the wide-angle end) increase. Although it is difficult to correct aberrations as they are, if a negative lens having an aspheric surface in which the power of the negative lens becomes weaker from the center to the periphery is arranged, more appropriate aberration correction can be performed. In the first and fourth embodiments, the convex-side surface of the negative meniscus lens is an aspheric surface, and the power (positive) of the surface increases (in the positive direction) from the center to the periphery. In the second embodiment, the object-side surface of the biconcave lens is an aspheric surface, and the power (negative) of the surface decreases from the center to the periphery. That is, in any of the first, second, and fourth embodiments, the aspherical surface of the negative lens used in the second lens group has a shape that reduces the negative power of the entire negative lens. ing.

  In addition, the negative lens having an aspheric surface (on at least one of the object side surface and the image side surface) in the second lens group is preferably disposed on the most image side in the second lens group. If a negative lens having an aspheric surface in the second lens group is disposed on the object side, the lens diameter increases, making manufacturing difficult, which increases costs. Further, it is advantageous for correcting off-axis aberrations (for example, distortion and curvature of field), but is disadvantageous for correcting on-axis aberrations. If a negative lens having an aspheric surface is arranged closest to the image side in the second lens group as in the first and fourth embodiments, these problems can be solved and high optical performance can be obtained. .

  As in the first, second, fourth, and fifth embodiments, it is preferable that the second lens group includes at least three negative lenses and at least one positive lens. If an attempt is made to widen the angle together with further zooming, it becomes difficult to correct the chromatic aberration of the second lens group, particularly to correct the chromatic aberration of magnification at the wide angle end. Normally, aberration correction is performed by using a low-dispersion negative lens. However, if the dispersion is low, the refractive index becomes low at the same time. Therefore, when the size is reduced, the surface power is increased. Increasing the power of the surface leads to a decrease in the radius of curvature, which results in an increase in the difficulty of processing, which is not preferable. If at least three negative lenses are used to disperse the negative power of the second lens group, the radius of curvature can be prevented from being reduced and chromatic aberration can be corrected appropriately.

Regarding the power of the third and fourth lens groups, it is desirable that the following conditional expression (4) is satisfied.
0.05 <f3 / f4 <0.8 (4)
However,
f3: focal length of the third lens group,
f4: focal length of the fourth lens group,
It is.

  Conditional expression (4) defines a preferable condition range regarding the power ratio between the third lens group and the fourth lens group. If the upper limit of conditional expression (4) is exceeded, the power of the fourth lens group will increase, resulting in an increased amount of aberration in the fourth lens group, and particularly good field curvature from the wide-angle end to the telephoto end. It becomes difficult to correct. Further, when focusing is performed by moving the fourth lens group, aberration fluctuations due to focusing, particularly field curvature fluctuations and chromatic aberration fluctuations, become large. In order to correct them satisfactorily, an additional number of lenses, an aspherical surface, and the like are required, which is not preferable. On the other hand, exceeding the lower limit of conditional expression (4) means that the power of the third lens group is increased or the power of the fourth lens group is decreased. As the power of the third lens group increases, the amount of aberration generated in the third lens group increases, and in particular, the amount of spherical aberration increases. In order to correct it satisfactorily, an additional number of lenses, an aspherical surface, and the like are required, which is not preferable. In addition, if the power of the fourth lens group is weakened, the overall length is enlarged, and when focusing is performed by moving the fourth lens group, the amount of movement of the fourth lens group during focusing becomes too large, which is not preferable. . In each embodiment, since the zoom configuration is suitable for performing focusing by moving the fourth lens group, it is preferable to satisfy the conditional expression (4).

It is more desirable to satisfy the following conditional expression (4a).
0.1 <f3 / f4 <0.5 (4a)
This conditional expression (4a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (4).

Regarding the power of the second lens group, it is desirable to satisfy the following conditional expression (5).
-0.2 <f2 / ft <-0.02 (5)
However,
f2: focal length of the second lens group,
ft: focal length of the entire system at the telephoto end,
It is.

  Conditional expression (5) defines a preferable condition range regarding the power of the second lens group by dividing the focal length of the second lens group by the focal length of the entire system at the telephoto end. If the upper limit of the conditional expression (5) is exceeded, the power of the second lens group becomes too strong, and the amount of aberration generated in the second lens group becomes large, and in particular, the field curvature and distortion become large. End up. In order to correct it satisfactorily, an additional number of lenses, an aspherical surface, and the like are required, which is not preferable. On the other hand, if the lower limit of conditional expression (5) is exceeded, it is advantageous in correcting aberrations, but the distance between the front and rear of the second lens group must be changed greatly during zooming, resulting in a large overall lens length. Therefore, it is not preferable.

It is more desirable to satisfy the following conditional expression (5a).
-0.10 <f2 / ft <-0.05… (5a)
This conditional expression (5a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (5).

  In the first, second, fourth, and fifth embodiments, a positive, negative, positive, positive, and positive five-component configuration is adopted in order from the object side, and zooming is performed during zooming from the wide-angle end to the telephoto end. The position is fixed. As described above, the zoom optical system has a five-component structure including the fifth lens group having a positive power on the image side of the fourth lens group. In the variable power from the wide angle end to the telephoto end, The positions of the five lens groups are preferably fixed. It is desirable that the principal ray incident on the image sensor is approximately perpendicular to the light-receiving surface of the image sensor (so-called telecentricity), but telecentricity becomes difficult to achieve if higher magnification and compactness are achieved. Become. In order to make the telecentricity good, it is preferable to have a fifth lens group with a fixed zoom position. In addition, the presence of the fifth lens group with a fixed zoom position can prevent dust from becoming a major problem in the electronic imaging device.

  As in the first, second, fourth, and fifth embodiments, it is preferable that the fifth lens group includes one positive lens. By constituting the fifth lens group with one positive lens, it is possible to prevent the enlargement of the total length and the cost increase due to the increase in the number of sheets and to obtain good telecentricity. Further, it is more preferable to form the fifth lens group with a single plastic lens, because cost reduction and weight reduction can be achieved.

  The zoom lens system ZL constituting each embodiment uses a refractive lens that deflects incident light by refraction (that is, a lens that deflects at the interface between media having different refractive indexes). However, the usable lens is not limited to this. For example, a diffractive lens that deflects incident light by diffracting action, a refractive / diffractive hybrid lens that deflects incident light by combining diffractive action and refracting action, and a refractive index distribution that deflects incident light by a refractive index distribution in the medium A mold lens or the like may be used. However, it is desirable to use a homogeneous material lens having a uniform refractive index distribution, because the refractive index distribution type lens whose refractive index changes in the medium increases the cost of its complicated manufacturing method. Further, in the zoom lens system ZL constituting each embodiment, a stop ST is used as an optical element in addition to the lens, but a light flux restricting plate (for example, a flare cutter) or the like for cutting unnecessary light is used. You may arrange | position as needed.

  Hereinafter, the configuration of the zoom lens system embodying the present invention will be described more specifically with reference to construction data and the like. Examples 1 to 5 listed here are numerical examples corresponding to the first to fifth embodiments, respectively, and are optical configuration diagrams showing the first to fifth embodiments (FIGS. 1 to 5). 5) shows the lens configurations of the corresponding Examples 1 to 5, respectively.

  Tables 1 to 10 show construction data of Examples 1 to 5, and Table 11 shows data such as values corresponding to conditional expressions of each example. In the basic optical configurations (i: surface number) shown in Table 1, Table 3, Table 5, Table 7, and Table 9, ri (i = 1, 2, 3,...) Is i from the object side. The radius of curvature (mm), di (i = 1, 2, 3,...) Of the i th surface is the axial upper surface distance (mm) between the i th surface and the (i + 1) th surface counted from the object side. ) And Ni (i = 1, 2, 3,...) And νi (i = 1, 2, 3,. The ratio (Nd) and the Abbe number (νd) are shown. Further, the axial top surface distance di that changes during zooming is a variable air distance from the wide-angle end (shortest focal length state, W) to the middle (intermediate focal length state, M) to the telephoto end (longest focal length state, T). , F, FNO respectively indicate the focal length (mm) and the F number of the entire system corresponding to each focal length state (W), (M), (T).

The surfaces marked with * in the data of the radius of curvature ri are aspherical surfaces (aspherical refractive optical surfaces, surfaces having a refractive action equivalent to aspherical surfaces, etc.), and represent the following aspherical surface shapes: It is defined by the formula (AS). In Table 2, Table 4, Table 6, Table 8, and Table 10, aspherical data of each example are shown. However, the coefficient of the term without description is 0, and E−n = × 10 ⁻ⁿ for all data.
X (H) = (C0 · H ² ) / {1 + √ (1−ε · C0 ² · H ² )} + Σ (Aj · H ^j ) (AS)
However, in the formula (AS)
X (H): Amount of displacement in the optical axis AX direction at the position of height H (based on the surface vertex),
H: height in a direction perpendicular to the optical axis AX,
C0: paraxial curvature (= 1 / ri),
ε: quadric surface parameter,
Aj: j-order aspheric coefficient,
It is.

  FIGS. 6 to 10 are aberration diagrams corresponding to Examples 1 to 5, respectively. (W) is the wide-angle end, (M) is the middle, and (T) is the infinite focus state at the telephoto end. Aberration {from left to right, spherical aberration, astigmatism, distortion, etc. FNO is the F number, and Y ′ (mm) is the maximum image height (corresponding to the distance from the optical axis AX) on the light receiving surface SS of the image sensor SR. }. In the spherical aberration diagram, the solid line d represents the d line, the alternate long and short dash line g represents the amount of spherical aberration (mm) with respect to the g line, and the broken line SC represents the unsatisfactory sine condition (mm). In the astigmatism diagram, the broken line DM represents the meridional surface, and the solid line DS represents each astigmatism (mm) with respect to the d-line on the sagittal surface. In the distortion diagram, the solid line represents the distortion (%) with respect to the d-line.

The lens block diagram of 1st Embodiment (Example 1). The lens block diagram of 2nd Embodiment (Example 2). The lens block diagram of 3rd Embodiment (Example 3). The lens block diagram of 4th Embodiment (Example 4). The lens block diagram of 5th Embodiment (Example 5). FIG. 6 is an aberration diagram of Example 1. FIG. 6 is an aberration diagram of Example 2. FIG. 6 is an aberration diagram of Example 3. FIG. 6 is an aberration diagram of Example 4. FIG. 6 is an aberration diagram of Example 5. FIG. 2 is a schematic diagram illustrating a schematic optical configuration example of a camera equipped with an imaging device.

Explanation of symbols

CU camera LU imaging device ZL zoom lens system (variable magnification optical system)
Gr1 1st lens group Gr2 2nd lens group Gr3 3rd lens group Gr4 4th lens group Gr5 5th lens group ST Aperture PT Parallel plane plate SR Image sensor SS Light receiving surface IM Image surface AX Optical axis

Claims (7)

A zooming optical system for forming an optical image of an object on a light-receiving surface of an image sensor so that zooming is possible, and in order from the object side, a first lens group having positive power and a first lens group having negative power Two lens groups, a third lens group having a positive power, and a fourth lens group having a positive power, and at least the first lens group and the third lens group move during zooming, A zoom optical system characterized in that the first lens unit moves toward the object side during zooming from the wide-angle end to the telephoto end, and satisfies the following conditional expressions (1), (2) and (3):
-0.5 <m2 / fw <5.0 (1)
7.0 <f1 / fw <20.0 (2)
0.05 <f3 / ft <0.4 (3)
However,
m2: Relative amount of movement of the second lens unit during zooming from the wide-angle end to the telephoto end (movement toward the object side is positive),
f1: focal length of the first lens group,
f3: focal length of the third lens group,
fw: focal length of the entire system at the wide-angle end,
ft: focal length of the entire system at the telephoto end,
It is.   2. The variable magnification optical system according to claim 1, wherein the second lens group includes at least one negative lens and one positive lens, and at least one of the negative lenses has an aspherical surface. The zoom lens system according to claim 1 or 2, wherein the following conditional expression (4) is satisfied:
0.05 <f3 / f4 <0.8 (4)
However,
f4: focal length of the fourth lens group,
It is. The zoom lens system according to any one of claims 1 to 3, wherein the following conditional expression (5) is satisfied:
-0.2 <f2 / ft <-0.02 (5)
However,
f2: focal length of the second lens group,
It is.   A variable power optical system having a five-component structure including a fifth lens group having a positive power on the image side of the fourth lens group, wherein the fifth lens is used for zooming from a wide angle end to a telephoto end. The zoom lens system according to any one of claims 1 to 4, wherein the position of the group is fixed.   6. The variable magnification optical system according to claim 5, wherein the fifth lens group includes one positive lens.   An imaging apparatus comprising the variable magnification optical system according to claim 1.

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